Other transition metal ions

The X-ray structure refinement of a synthetic Mg-Co2+ olivine (Ghose and Wan, 1974 Ghose et al., 1975) show that Co2+ ions also favour the Ml sites. The Xddata plotted in fig. 6.3 indicate that cobalt is less strongly enriched than Ni2+ ions in the Ml sites. The X-ray structure refinements (Ghose et al., 1975) and Kd data plotted in fig. 6.3 show that Zn2+ ions also favour the olivine Ml sites. 

In a synthetic forsterite doped with 2x Kfr per cent chromium, Cr3 ions were shown by EPR measurements (Rager, 1977) to be slightly enriched in the Ml sites resulting in an occupancy ratio M1 M2 = 60 40, corresponding to 1.2 xl(H per cent Cr3+ in the Ml site. In ferric-bearing forsterites, EPR measurements indicated that Fe3+ ions have a preference for the M2 sites (Weeks et al., 1974). 

The crystal field spectral measurements of orthopyroxenes described in 5.5.4 also demonstrate the relative enrichments of Fe2+ ions in the pyroxene M2 sites (Goldman and Rossman, 1979). 

In pigeonites, X-ray diffraction (e.g., Clark et al., 1971 Brown et al., 1972 Takeda et al., 1974) and Mossbauer spectral measurements (Bancroft and Bums, 1967b) of samples from lunar and volcanic rocks demonstrate that there is a strong enrichment of Fe2+ ions in the M2 sites, but the enrichments are slightly smaller than those in metamorphic orthopyroxenes with similar iron contents due, in part, to the higher Ca contents of pigeonites. 

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The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

Cobalt exists in the +2 or +3 valence states for the majority of its compounds and complexes. A multitude of complexes of the cobalt(III) ion [22541-63-5] exist, but few stable simple salts are known (2). Werner s discovery and detailed studies of the cobalt(III) ammine complexes contributed gready to modem coordination chemistry and understanding of ligand exchange (3). Octahedral stereochemistries are the most common for the cobalt(II) ion [22541-53-3] as well as for cobalt(III). Cobalt(II) forms numerous simple compounds and complexes, most of which are octahedral or tetrahedral in nature cobalt(II) forms more tetrahedral complexes than other transition-metal ions. Because of the small stabiUty difference between octahedral and tetrahedral complexes of cobalt(II), both can be found in equiUbrium for a number of complexes. Typically, octahedral cobalt(II) salts and complexes are pink to brownish red most of the tetrahedral Co(II) species are blue (see Coordination compounds). 

The versatile binding modes of the Cu2+ ion with coordination number from four to six due to Jahn-Teller distortion is one of the important reasons for the diverse structures of the Cu-Ln amino acid complexes. In contrast, other transition metal ions prefer the octahedral mode. For the divalent ions Co2+, Ni2+, and Zn2+, only two distinct structures were observed one is a heptanuclear octahedral [LnM6] cluster compound, and the other is also heptanuclear but with a trigonal-prismatic structure. 

The Cr+ and Mn+ ions have ground-state electronic configurations 3<754.v° and 3d54s1, respectively, and both react slowly (relative to other transition metal ions) with S8 but do not react with P4 (whereas other transition metal ions react readily). The Ca+ (3d°4s1) ion reacts rapidly with S8 (98) (more rapidly than most bare transition metal ions) but reacts very slowly with P4 producing the [CaP]+ ion. The Ba+ ion also reacts readily with S8 but is unreactive to P4 (99). These observations indicate that the electronic configuration of the metal ion and the properties of the reacting molecule are important in determining reactivity. The formation of stable product ions is also important. Whereas most transition metals react with S8 to produce [MS4]+ ions, the product ion for Ca+ and Ba+ is the [MS3]+ ion. 

Silver ions (as silver trifluoroacetate or trifluoromethanesulfonate), Cu", and other transition metal ions in their 1h- oxidation state [99,100] are frequently employed to obtain [M-rmetal] ions from non-functionalized or at least nonpolar hydrocarbons, [101] polyethylene, [102,103] or polystyrene (for an example see Chap. 10.5.1). [99,100,104-106]... 

Using chemistry similar to that just discussed for Cu +, we have shown that many other transition metal ions, including Pd +, Pt +, Ni +, and Ru +, can be extracted into the dendrimer interiors [59,83,84]. For example, a strong absorption peak at 250 nm ( =8000 cm ) arising from a ligand-to-metal-charge-transfer... 

E. Other transition metal ions complexes and proteins 158... 

E. Other Transition Metal Ions Complexes and Proteins... 

In the following sections we will review the copper complexes of the various classes of aminoglycosides described earlier. Discussion will focus on complexes that are formed at physiological pH (7.4) but will take into account the differing modes of coordination at other pH values, as well as accounting for the distinct binding modes of other transitions metal ions. 

Cobalt(II) forms more tetrahedral complexes than any other transition metal ion. Also, because of small energy differences between the tetrahedral and octahedral complexes, often the same ligand forms both types of Co(II) complexes in equilibrium in solutions. 

The reduction of Cu to Cu in the zeolite lattice is more difficult than reduction of platinum and palladium ions but easier than that of other transition metal ions.25 The resulting Cu" " ion in the zeolite is fairly stable both in a reductive atmosphere and imder degassing treatment at elevated temperatures, wh eas the precious metal ions are easily reduced to the respective metals and collect to yield metal particles. Die easy reducibility of Cu and the stability of Cu" " lead to a reversible redox behaivor betweoi Cu and Cu and result in the iqipearance of the specific catalytic activity. 

Reaction (63) is an example of 0 acting as an oxidant and it probably proceeds via an inner-sphere electron transfer mechanism in which incompletely coordinated Cu binds O2 prior to electron transfer [87]. HO2 and 0 also react readily with a number of other transition metal ions, either by electron transfer or through the formation of a complex [83], for example ... 

Substitution of other transition metal ions for Cu, however, was observed (174) to be highly deleterious to superconducting behavior. Table 14 shows the results of 10% metal-ion substitution in the Cu sites. 

A-Vinylpyrrolidone polymers are of special interest in medicine in the process of detoxification as well as for binding and removal of undesirable metallic ions and known as chelatotherapeutic agents [34]. Free radical copolymers of poly(lV-vinylpyrrolidone) and copolymer of JV-vinylpyrrolidone and vinylacetate, vinylamine, vinylamidosuceinic arid are known to bind Cu2+ and other transition metal ions, and the resultant complexes exhibit interesting physico-chemical properties. 

CrOl ) reasonably stable the Cr(I) oxidation stale is practically unknown. For both Cu2 and Cr3 (as well as many other transition metal ions) ligand field effects in their complexes (see Chapter II) are much more important in determining stable oxidation states than are electron configurations. 

The zinc-ion-catalyzed aquation of cis-[Cr(H20)2L2]+ (HL = CH2(C02H)2) has been shown to obey a rate law of the type in equation (10), although other transition metal ions are more effective catalysts.1223... 

It is surprising that the adsorption of Co2+ is anomalous when compared with other transition metal ions in that Co(II) and Ni(II) and to a lesser extent Cu(II) are very similar chemically. It is known (8) that certain metal ions can be catalytically oxidized on metal electrodes. It may therefore be possible for Co2+ in the present system to be oxidized to Co8+ in the region of the Mn02-water interface. Although this suggestion has... 

One form of antioxidant defense may be the binding of excess Fe3+ and other transition metal ions, preventing Fe3+, and other transition metal pro-oxidants from catalyzing free radical reactions. Most intracellular Fe3+ is stored in ferritin. Mammalian ferritins consist of a hollow protein shell 12-13 nm outside diameter... 

Interesting results have been obtained in studies of the catalytic activity for oxidation by phthalocyanine polymers, containing different metal ions in the same molecule 87-90>. If Fe was mixed with a series of other transition metal ions, differences in activity were found to be dependent on the metal ion, and correlations between the catalytic activity and the thermal activation energy of semiconductivity were found. With copper as the second metal ion, maximum activities were found at a ratio Fe/Cu = 1. Many other chelate polymers have been tested for their oxidation activity, and a dependence of the catalytic activity on the donor properties of the ligand was found 91>92). 

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